Ozone is a gas with strong oxidizing properties. It is commonly generated by forcing oxygen or air through narrowly spaced electrodes under a high voltage, known as the corona discharge method. The first commercial uses of ozone occurred in Europe in the late 1890's for the treatment of drinking water. Since then, ozone has been widely used for both the treatment of drinking water and wastewater.
Ozone can react with organic contaminants via two general pathways: a) direct oxidation; and b) oxidation through the formation of free radical intermediaries. The most common radical pathway utilizes hydroxyl radicals. Contaminants most amenable to direct oxidation include polynuclear aromatic hydrocarbons, chlorinated ethenes such as trichlorethylene, and chlorinated phenols such as pentachlorophenol (PCP). A wider range of organic contaminants, including halogenated solvents, pesticides and aliphatic hydrocarbons, can be oxidized slowly by direct oxidation or more rapidly oxidized by the hydroxyl radical mechanism. Following only fluorine, which has an oxidation potential of 3 volts, hydroxyl radicals (oxidation potential of 2.96 volts) and ozone (oxidation potential 2.07 volts) are the second and third strongest oxidants known.
At many industrial and commercial facilities throughout the United States, soil and groundwater have become contaminated with organic pollutants. Accidental spills have occurred at other sites contaminating both soil and groundwater. A variety of techniques have been developed for the removal of these contaminants. One common technique is soil excavation and off-site treatment of the soil, which is often very expensive. Another treatment involves air sparging technology using the controlled injection of air to strip organic compounds from the water or to supply oxygen for bioremediation of the contaminants. However, chlorinated olefins and complex aromatics are often resistant to sparging and bioremediation, thereby requiring more complex and expensive treatments.
Ozone has been shown to be an effective oxidant in the treatment of organic contaminants in solid matrices such as soils (both saturated and unsaturated) and sludges. Previously, the successful treatment of contaminated solid matrices has involved the continuous application of ozone. Experience with this approach has demonstrated that persistent, continuous ozonation of a contaminated solid matrix can be an effective way of treating a wide range of organic contaminants contained within the solid matrix. Because ozonation is a direct chemical reaction, the rate and effectiveness is expected to be proportional to the mass of ozone added (weight percent, flow and time). The higher the ozone mass, the more effective the reaction with the contaminants is expected to be.
While continuous ozonation of solid matrices containing organic contaminants is effective, it is also very expensive. Ozone generators are costly not only to purchase but also to operate. Ozone generators require a lot of power. As a result of the high cost of using continuous ozonation to treat solid matrices containing organic contaminants, ozonation is not often a reasonable choice when evaluating the options available for cleaning up a particular contaminated site.
It has been known that a single application of ozone could improve the biodegradability of contaminants. This approach involved using a single stage of ozone treatment followed by biological treatment of the contaminants. Since ozone is a microbial sterilant, there has always been the concern that the ozone pretreatment would negatively impact or even completely destroy the biodegradation phase by destroying the microbes upon which biodegradation relies.
It is an object of the present invention to provide a method of treating a solid matrix containing organic contaminants by using ozone. It is a further object of this invention to provide a cost effective method of treating a solid matrix containing organic contaminants by using ozone in an efficient manner. Other objects of the present invention will appear from the disclosure presented herein.